This invention relates generally to the rendering of latent electrostatic images visible. More particularly, the invention relates to delivering highly charged toner containing a low quantity of wrong sign toner to a donor roll structure.
The invention can be utilized in the art of xerography or in the printing arts. In the practice of conventional xerography, it is the general procedure to form electrostatic latent images on a xerographic surface by first uniformly charging a photoreceptor. The photoreceptor comprises a charge retentive surface. The charge is selectively dissipated in accordance with a pattern of activating radiation corresponding to original images. The selective dissipation of the charge leaves a latent charge pattern on the imaging surface corresponding to the areas not exposed by radiation.
This charge pattern is made visible by developing it with toner. The toner is generally a colored powder which adheres to the charge pattern by electrostatic attraction. In accordance with the present invention, a donor roll structure is utilized in the process of forming visible images.
The developed image is then fixed to the imaging surface or is transferred to a receiving substrate such as plain paper to which it is fixed by suitable fusing techniques.
Alternatively, the present invention can be utilized in a direct electric printer (DEP) system. In a DEP printer, a donor structure in the form of a roll is used to deliver toner particles to an apertured printhead through which toner particles are deposited in image configuration on plain paper. Apertures are selectively addressed in accordance with information to be printed.
U.S. Pat. No. 4,814,796 granted to Fred W. Schmidlin on Mar. 21, 1989 relates to a direct electrostatic printing apparatus including structure for delivering developer or toner particles to a printhead forming an integral part of the printing device. The printing device includes, in addition to the printhead, a conductive shoe which is suitably biased during a printing cycle to assist in the electrostatic attraction of developer through apertures in the printhead onto the copying medium disposed intermediate the printhead and the conductive shoe. The structure for delivering developer or toner is adapted to deliver toner containing a minimum quantity of wrong sign toner. To this end, the developer delivery system includes a conventional magnetic brush which delivers toner to a donor roll structure which, in turn, delivers toner to the vicinity of apertures in the printhead structure.